AU706366B2 - Multi-position guide bar fastening - Google Patents

Description

WO 97/19794 PCT/SE96/01471 Multi-position guide bar fastening Backmound Chain saw guide bars are normally attached to the machine unit of a chain saw by two threaded bolts penetrating a longitudinal slot through the rear end of the guide bar, defining the direction of the guide bar, but allowing a longitudinal displacement which is needed when replacing a saw chain or compensating for wear of the chain.

Commonly, the guide bar is symmetric with the slot symmetrically located on the center line, making it possible to turn the guide bar over to wear both sides of the bar equally.

Behind the guide bar is a drive shaft with a drive sprocket for the chain.The bolts are often located to let the bar center line pass through the drive shaft, as in the patents US 3,683,980 and US 3,955,279, but it is also known to let the center line pass below the shaft as in patents US 2,845,967, US 2,910,100 and US 3,059,491 to allow a larger deflection of the slack upper part of the chain. With introduction of self-tensioning drive sprockets as shown in patent DE 41 37 4009 or SE 469 515 it has also been suggested to let the bar centerline pass above the drive shaft.

The present invention is a mounting arrangement for chain saw guide bars, allowing the bar center line to pass above, straight through or below the drive shaft according to the service conditions.

Description of the invention The invention is described with reference to the figures, where figure 1 shows a guide bar mounted with the center line above the drive shaft, and figures 2 4 show different embodyments of slot inserts according to the invention.

A saw chain (19) is driven by a drive sprocket (12) on a drive shaft to travel around a guide bar The drive sprocket carries an outer drive ring (13) the center of which will occupy an equilibrium position above the drive shaft when sawing. The saw machine unit is provided with two bolts and the line (15) through the bolts passes also through WO 97/19794 PCT/SE96/01471 2 the shaft of the drive sprocket To make the chain pass smoothly from the drive ring (13) to the upper side of the guide bar (11) the bar center line (16) has been displaced upwards relative to the line (15) through the bolts To accomplishthis, the guide bar is made with a slot (14) which is substantially wider than the bolt (18) diameter. The slot is preferably symmetrically located on the bar to allow reversing of the bar when worn.

In the slot (14) are placed one or more inserts (17) with holes to receive the bolts (18).

The inserts can either be turned in different directions, or have several holes differently located in relation to the center line (16) of the slot. In figure 1 the inserts (17) are turned with the holes for the bolts (18) below the slot center line. Figure 2 shows how such square inserts can be turned into at least three positions with the holes below, above or on the center line (16).

Figure 3 shows an insert with four holes, two of which (22) on the center line (16) and two (21) offset from the center line. By reversing the insert, teh offset holes (21) can be located below or above the center line. If the space is very restricted, the holes may touch or slightly intersect each other.

Traditionally the guide bar is attached to the machine unit by fitting a clamping plate with two bolt holes outside the guide bar. The clamping plate is wider than the slot (14) and with one nut on each bolt the clamping plate and the guide bar are fastened to the machine unit. If one wishes to use such an existing clamping plate because it is part of or coacts with the machine cover, the inserts should have a thickness not exceeding the guide bar (11) thickness.

In certain cases such as when mounting a guide bar on a vehicle-born chain saw, the clamping plate may have functions related to the guide bar geometry, such as connectmatching certain liquid supply channels, or providing an auxiliary chain guide. In such cases the clamping plate position relative to the bar should be retained, and the clamping plate should have four holes and could be made integral with a four hole (21,22) insert as shown in figure 4. To ensure stiff clamping, the insert should have a thickness not exceeding the bar thickness.

Claims (7)

1. Clamping device for mounting a chain saw guide bar to two threaded bolts (18) protruding from a chain saw machine unit with the guide bar center line parallel to but offset from a line through the bolts, characterized by the guide bar having a longitudinal slot (14) with a width substantially larger than the bolt diameter, and with at least one insert (17) being located in the slit, said insert having the same width as the slot (14) and at least one hole (21,22) fitting a bolt, said insert being locatable in at least one position where the holes are offset from the center line (16) of the slot.

2. Clamping device according to claim 1, characterized by the insert being locatable in another position where the holes are on the center line (16) of the slot.

3. Clamping device according to claim 1 or 2, characterized by the slot (14) being symmetrically located in the guide bar.

4. Clamping device according to claim 1 or 2, characterized by there being two square inserts (17) in the slot, each insert having one off-center hole located closer to one side.

5. Clamping device according to claim 1 or 2, characterized by there being one insert (17) in the slot, said insert having four holes (21,22).

6. Clamping device according to claim 5, characterized by two holes (22) being located on the center line (16) of the insert, and two holes (21) offset from the center line.

7. Clamping device according to claim 6, characterized by the insert (17) being integral with a clamping plate (20) which is wider than the slot (14).